The hydrogen sulfide content of fluids from oil and gas wells has an important impact on the economic value of the produced hydrocarbons and production operations. Hydrogen sulfide is dangerous to personnel as it is extremely toxic to humans and is extremely corrosive to most metals. It can cause corrosion problems to drill strings, transport pipes, storage tanks, and other metal components. It causes sulfide stress cracking, hydrogen embrittlement and pitting corrosion in oil and gas operations. The removal of hydrogen sulfide from oil and gas streams is often required in order to meet many pipeline and storage regulations.
A number of processes are available to remove hydrogen sulfide from hydrocarbon streams using chemical agents. These chemical agents react with one or more sulfide species and convert them to a more inert form. These chemical agents are known in the industry as sulfur scavengers. Sulfur scavengers can be in a solid or liquid form. Liquid scavengers may be regenerative scavengers such as amine wash or reduction oxidation or non-regeneration scavengers such as aldehydes, triazines, and sodium nitrates, as examples. When the hydrogen sulfide concentration is low, non-regenerative liquid scavengers are often used.
A large number of non-regenerative chemical formulations exist for removal of hydrogen sulfide. One important group and the most frequently used liquid hydrogen sulfide scavengers are hexahydrotriazine-based hydrogen sulfide scavengers. These are commonly referred to in the industry as triazine scavengers. Triazines are readily deployed in scrubbers and are effective scavengers. Triazine is a heterocyclic structure similar to cyclohexane but with three carbons replaced by nitrogen atoms. The most common triazines used as hydrogen sulfide scavengers are monoethanolamine (MEA triazine) or methyl amine (MA triazine). Variations involving substitutions of the hydrogen atoms with other functional groups are used and different substitutions result in different reactivity with hydrogen sulfide, changes in the solubility of the triazine, and changes in the solubility of the reactant products. Triazine can therefore be tailored to better suit the application.
In one example, a liquid hydrogen sulfide scavenger, such as triazine, is used in a contactor tower or scrubber. The hydrocarbon feed gas is bubbled through the tower filled with an aqueous fluid containing triazine. As the hydrocarbon gas bubbles up through the aqueous based fluid, the hydrogen sulfide reacts with the triazine and the hydrogen sulfide is removed from the hydrocarbon gas stream.
The main byproduct of reacted triazine is dithiazine. Dithiazine is the result of two moles of hydrogen sulfide reacting with one mole of triazine. Dithiazine is easy to handle and dispose of. If the reaction proceeds further, a solid polymeric material believed to be a thioformaldehdye polymer substitution on the dithiazine molecule is formed. This solid material is hard to handle and dispose of, and can cause operational difficulties in scrubbing towers. Hence it is desirable from a cost perspective to maximize the formation of dithiazine while monitoring the progress of the reaction in order to minimize solids formation.
As a result, it is useful to be able to determine the amount of and efficiency of hydrogen sulfide scavenger in a system to be able to determine whether more or less scavenger should be added to the system. It would be useful to have a portable apparatus and a rapid testing method for determining the amounts of hydrogen sulfide scavenger and its byproducts in the liquid in the scrubber or contact tower.
Currently, there are limited options for rapid, portable techniques for measuring how much capacity is remaining in the scavenger as it is flowed through a scrubber or contactor tower. To measure sulfur in spent scavenger, a common method is combustion analysis. This method requires special equipment which is often difficult to set up in remote locations and if the equipment is not available on site, the transportation of samples can significantly delay analysis. As a result, it can be difficult to use this process for real time adjustments to a scavenging system. Other methods may be available on site but would require hours to conduct an analysis of samples or the results are not accurate.
While several products are available for detecting the level of hydrogen sulfide in crude oil, there are limited options for the effective and rapid determination of hydrogen sulfide scavengers in aqueous-based fluids.
It is, therefore, desirable to provide a portable apparatus and method for the rapid determination of hydrogen sulfide scavenger in an aqueous based sample.